Glycoprotein Immunoassay to Measure Protective Humoral Responses to Lassa Vaccine This project will complete the pre-clinical development of a Lassa virus (LASV) glycoprotein immunoassay to measure the protective response to Lassa fever (LF) vaccines. LF causes endemic febrile illness throughout West Africa and can quickly progress to viral hemorrhagic fever with mortality rates greater than 50% in high risk groups. LASV is transmitted to humans through exposure to the excreta of its rodent host or direct contact with bodily fluids of an active LF case. The West African population and non-indigenous groups such as deployed US military are at increased risk of zoonotic LF transmission. This companion diagnostic will fill the unmet need for a standardized assay to measure the humoral response to Lassa virus infection in humans and non-human primates and prescreen study candidates and monitor their response to Lassa virus glycoprotein based vaccines now under development. The enzyme labeled immunosorbent assay (ELISA) format test will incorporate highly specific reagents recently developed to advance Lassa fever therapeutics and vaccines. Our proprietary ELISA plate coating will specifically absorb and stabilize trimeric LASV glycoprotein developed at the Scripps Research Institute. This recombinant glycoprotein has been specially engineered to replicate the neutralizing and non- neutralizing epitopes of LASV currently causing Lassa fever outbreak in West Africa. Identification of these epitopes was completed through the use of recombinant human monoclonal antibodies (HuMabs) derived by researchers at Tulane University and Zalgen Labs from B cells donated by Lassa fever survivors in West Africa. Several of these HuMabs have been combined into the therapeutic Arenviramab-3 (Zalgen Labs) and recently shown to completely protect NHPs from fatal inoculations of LASV. The proposed glycoprotein ELISA test will include these HuMabs as reference standard to accurately measure the level of human (and NHP) antibody response to LASV vaccine. The first aim of this project will be to complete design optimization of the Lassa GPC Antibody ELISA test including freeze-dried reference standards, controls, and kit packaging for eventual deployment to West African clinical sites. The second aim of the program will completion of pilot stage kit manufacturing and design validation analytical performance testing. The third aim will be verification of sensitivity and specificity estimates by testing both non-human primate and de-identified human diagnostic samples from biorepositories in both Sierra Leone and Nigeria. Our ultimately goal is a regulatory approved product to support Lassa fever therapeutic and vaccine development studies and assist in the deployment of these lifesaving interventions throughout West Africa and to other at risk groups.